1. Field of the Invention
The present invention relates to communication devices and high-frequency couplers for large-capacity data transmission in close proximity through a weak UWB communication technique using a high-frequency wide band and, in particular, to a communication device and high-frequency coupler of low height.
2. Description of the Related Art
Non-contact communication has been widely available as a medium for authentication information, electronic money, and other value information. Examples of an IC card standard complying with ISO/IEC 14443 include Type A, Type B, and FeliCa®. Furthermore, near field communication (NFC) developed by Sony Corporation and Koninklijke Philips Electronics N.V. is an RFID standard mainly defining specifications of an NFC communication device (reader/writer) communicable with an IC card of each of Type A, Type B, and FeliCa. In NFC, with the use of a band of 13.56 MHz, non-contact bidirectional communication of a close-proximity type (0 or more but 10 or less cm) can be performed through electromagnetic induction.
In recent years, a reader/writer module of a compact size suitable for incorporation has been developed and manufactured, and can be used as being implemented for use in various devices, such as a point of sales (POS) terminal, vending machine, and personal computer. For example, an information processing device of a notebook type is suggested in which a reader/writer module is incorporated in a palm rest portion of a keyboard of a main body and information is read from a non-contact IC tag nearby (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-87263).
An example of a further application of a non-contact communication system is large-capacity data transmission, such as downloading or streaming of moving pictures and music. For example, it can be assumed that non-contact communication is used when a fee-based content is downloaded from a vending machine to a portable terminal or when a content is downloaded from a fee-based site to a portable terminal via a personal computer connected to the Internet. In this case, it is preferable that a single user operation of holding the portable terminal over a read surface suffices and the operation completes with the sense of the same access time as that for authentication and billing in the past. Therefore, a high communication rate is desired.
However, the communication rate in NFC communication, which is a typical example of non-contact communication, is approximately 106 kbps to 424 kbps, which is sufficient for personal authentication or billing process but is extremely slow compared with other general-purpose wireless communication (such as WiFi and Bluetooth). Also, in the technique in the past, such as NFC communication, an achievable maximum communication rate is up to 848 kbps at best, due to physical constraints, such as carrier frequency. Thus, it is difficult to expect a dramatic increase in rate in the future.
By contrast, an example of a close-proximity wireless transfer technology applicable to high-speed communication is TransferJet using a weak ultra wide band (UWB) signal (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-99236 and www.transferjet.org/en/index.html (as of Mar. 23, 2009)).
The above-mentioned close-proximity wireless transfer technology (TransferJet) is of a technique of basically transmitting a signal by using an electric-field coupling action, and a communication device for the technique includes a communication circuit unit processing a high-frequency signal, a coupling electrode disposed so as to be separated from a ground at a predetermined height, and an resonating unit efficiently supplying the high-frequency signal to the coupling electrode. As with the non-contact IC tag described above, when the communication device is implemented on an information device for use, it can be one of important technical problems to lower the height of the weak UWB communication device.